John James Barry

Bio: John James Barry is an academic researcher from University College Dublin. The author has contributed to research in topics: Machining & Chip formation. The author has an hindex of 12, co-authored 34 publications receiving 983 citations. Previous affiliations of John James Barry include Kennametal.

Observations on chip formation and acoustic emission in machining Ti–6Al–4V alloy

Abstract: Orthogonal cutting tests were undertaken to investigate the mechanisms of chip formation for a Ti–6Al–4V alloy and to assess the influences of such on acoustic emission (AE). Within the range of conditions employed (cutting speed, v c =0.25–3.0 m/s , feed, f=20–100 μm ), saw-tooth chips were produced. A transition from aperiodic to periodic saw-tooth chip formation occurring with increases in cutting speed and/or feed. Examination of chips formed shortly after the instant of tool engagement, where the undeformed chip thickness is slightly greater than the minimum undeformed chip thickness, revealed a continuous chip characterised by the presence of fine lamellae on its free surface. In agreement with the consensus that shear localisation in machining Ti and its alloys is due to the occurrence of a thermo-plastic instability, the underside of saw-tooth segments formed at relatively high cutting speeds, exhibiting evidence of ductile fracture. Chips formed at lower cutting speeds suggest that cleavage is the mechanism of catastrophic failure, at least within the upper region of the primary shear zone. An additional characteristic of machining Ti–6Al–4V alloy at high cutting speeds is the occurrence of welding between the chip and the tool. Fracture of such welds appears to be the dominant source of AE. The results are discussed with reference to the machining of hardened steels, another class of materials from which saw-tooth chips are produced.

TEM study on the surface white layer in two turned hardened steels

Abstract: The structure of surface white layers was examined using transmission electron microscopy. Surface specimens were machined from a BS 817M40 steel (0.4C 1.2Cr 1.4Ni 0.2Mo) of 52 HRC and a low alloy tool steel (0.8C 1.7Cr 0.4Mo) of 58 HRC, with unworn and worn alumina/TiC composite cutting tools. Thin foil specimens were prepared such that the direction of observation was normal to the machined surface. The as-tempered microstructure of both steels was lath martensite. The structure of the machined surfaces of both steels was characterised by very fine, mis-orientated cells, less than 100 nm in size. The accompanying selected area electron diffraction patterns indicated the presence of retained austenite, the volume fraction of which increased with cutting tool wear. A refinement in the size of cementite particles was also evident. In the surface of the BS 817M40 steel machined with a worn cutting tool, there was evidence to suggest a degree of recrystallization. This may be accounted for by a transition from dynamic recovery to dynamic recrystallization during surface generation; a phenomenon which is favoured by the decrease in the work materials stacking fault energy as a result of the reverse martensite transformation.

The mechanisms of chip formation in machining hardened steels

Abstract: The formation of saw-tooth chips is one of the primary characteristics in the machining of hardened steels with geometrically defined cutting tools. Catastrophic failure within the primary shear zone during saw-tooth chip formation is usually attributed to either cyclic crack initiation and propagation or to the occurrence of a thermo-plastic instability. The results presented here show that the primary instability resulting in the formation of saw-tooth chips is initiation of adiabatic shear at the tool tip and propagation partway towards the free surface. Depending on the work material hardness and cutting conditions, catastrophic failure within the upper region of the primary shear zone occurs through either ductile fracture or large strain plastic deformation. Prior to the onset of chip segmentation, which occurs with increases in work material hardness and cutting speed, there is a transition in the morphology of the free surface of continuous chips, from the familiar lamellar structure to what has been termed a fold-type structure. This transition is attributed to the operation of thermally softened micro-shear zones, which, it is suggested, are a precursor to adiabatic shear initiation.

Cutting tool wear in the machining of hardened steels: Part I: alumina/TiC cutting tool wear

Abstract: A study was undertaken to investigate the mechanisms of alumina/TiC cutting tool wear in the finish turning of hardened steels with particular cognisance of the work material inclusion content. A six-fold variation in tool life was observed when machining different heats of BS 817M40 steel (similar to AISI 4340) of 52 HRC. In machining steels containing Ca-bearing mixed oxide inclusions, a reaction between the alumina phase of the tool and oxide inclusionary deposits is the dominant wear mechanism. In machining steels containing very low levels of Ca or steels with a very low inclusion content, tool wear appears to be largely based on superficial plastic deformation of the tool surface. The rate of tool wear appears to be determined by the hard inclusion content or alloy carbide content of the work material. Impingement of hard particles against the tool surface are thought to result in the generation of transient localised stresses which exceed the average contact pressures and, thus, either facilitate the operation of additional slip systems or overcome the increases in the critical resolved shear stresses on active slip systems due to prior strain. The influence of saw-tooth chip formation on cutting tool wear is also considered.

Cutting tool wear in the machining of hardened steels

Abstract: A study was undertaken to investigate the wear mechanisms of CBN/TiC cutting tools in the finish machining of BS 817M40 (AISI 4340) steel of 52 HRC. A fourfold variation in tool wear rate was observed in the machining of three different heats of this steel. One of the primary characteristics of the tool wear surfaces is the manner in which the TiC phase stands proud of the CBN phase. The relative abundance of different elements on the wear surfaces of the tools, which are present in the work material in small (Mn, Si) or very small (Al, S, O) quantities, suggests that the dominant wear mechanism of CBN/TiC cutting tools is chemical in nature. In considering the relative wear rates of the tools used to machine the different heats of steel, a reasonable correlation is noted between the work material Al and S content and the corresponding tool wear rate. Examination of built up layers at the trailing edge of the tool, however, suggests that work material Al content is rate-determining with regards to tool wear. Following these observations, a new mechanism is proposed to account for the (widely acknowledged) superior wear resistance of CBN/TiC composites in comparison to high-content CBN tools.

An overview of the machinability of aeroengine alloys

Abstract: Advanced materials such as aeroengine alloys, structural ceramics and hardened steel provide a serious challenge for cutting tool materials during machining due to their unique combinations of properties such as high temperature strength, hardness and chemical wear resistance. Although these properties are desirable design requirements, they pose a greater challenge to manufacturing engineers due to the high temperatures and stresses generated during machining. The poor thermal conductivity of these alloys result in concentration of high temperatures at the tool–workpiece interface. This is worsened at higher cutting conditions because of the significant reduction in the strength and hardness of the cutting tool. This weakens the bonding strength of the tool substrate, thereby accelerating tool wear by mechanical (abrasion and attrition) and thermally related (diffusion and plastic deformation) mechanisms. Therefore, cutting tools used for machining aerospace materials must be able to maintain their hardness and other mechanical properties at higher cutting temperatures encountered in high speed machining. Tool materials with improved hardness like cemented carbides (including coated carbides), ceramics and cubic boron nitride (CBN) are the most frequently used for machining aeroengine alloys. Despite the superior hardness and cutting performance of CBN tools, ceramic tools are generally preferred for high speed continuous machining because of their much lower cost. Improvements in machining productivity can also be achieved with the latest machining techniques such as ramping or taper turning and rotary machining. These techniques often minimise or completely eliminate the predominant notching of the cutting tools, consequently resulting in catastrophic fracture of the entire cutting edge when machining aeroengine alloys.

Surface integrity in material removal processes: Recent advances

Abstract: This paper is a result of a three-year study by the CIRP's Collaborative Working Group on Surface Integrity and Functional Performance of Components, and it reports recent progress in experimental and theoretical investigations on surface integrity in material removal processes Experimental techniques for measuring various surface integrity parameters are presented Results from a Round Robin Study on surface integrity parameters such as residual stresses, hardness and roughness in turning, milling, grinding, and EDM, are then presented Finally, results and analysis of a benchmarking study comparing available predictive models for surface integrity are presented, followed by concluding remarks and future research directions

Radiative Forcing of Climate Change

Abstract: Our current understanding of mechanisms that are, or may be, acting to cause climate change over the past century is briefly reviewed, with an emphasis on those due to human activity. The paper discusses the general level of confidence in these estimates and areas of remaining uncertainty. The effects of increases in the so-called well-mixed greenhouse gases, and in particular carbon dioxide, appear to be the dominant mechanism. However, there are considerable uncertainties in our estimates of many other forcing mechanisms; those associated with the so-called indirect aerosol forcing (whereby changes in aerosols can impact on cloud properties) may be the most serious, as its climatic effect may be of a similar size as, but opposite sign to, that due to carbon dioxide. The possible role of volcanic eruptions as a natural climate change mechanism is also highlighted.

Predictive modeling of surface roughness and tool wear in hard turning using regression and neural networks

Abstract: In machining of parts, surface quality is one of the most specified customer requirements. Major indication of surface quality on machined parts is surface roughness. Finish hard turning using Cubic Boron Nitride (CBN) tools allows manufacturers to simplify their processes and still achieve the desired surface roughness. There are various machining parameters have an effect on the surface roughness, but those effects have not been adequately quantified. In order for manufacturers to maximize their gains from utilizing finish hard turning, accurate predictive models for surface roughness and tool wear must be constructed. This paper utilizes neural network modeling to predict surface roughness and tool flank wear over the machining time for variety of cutting conditions in finish hard turning. Regression models are also developed in order to capture process specific parameters. A set of sparse experimental data for finish turning of hardened AISI 52100 steel obtained from literature and the experimental data obtained from performed experiments in finish turning of hardened AISI H-13 steel have been utilized. The data sets from measured surface roughness and tool flank wear were employed to train the neural network models. Trained neural network models were used in predicting surface roughness and tool flank wear for other cutting conditions. A comparison of neural network models with regression models is also carried out. Predictive neural network models are found to be capable of better predictions for surface roughness and tool flank wear within the range that they had been trained. Predictive neural network modeling is also extended to predict tool wear and surface roughness patterns seen in finish hard turning processes. Decrease in the feed rate resulted in better surface roughness but slightly faster tool wear development, and increasing cutting speed resulted in significant increase in tool wear development but resulted in better surface roughness. Increase in the workpiece hardness resulted in better surface roughness but higher tool wear. Overall, CBN inserts with honed edge geometry performed better both in terms of surface roughness and tool wear development. q 2004 Elsevier Ltd. All rights reserved.

The effect of machining on surface integrity of titanium alloy Ti–6% Al–4% V

Abstract: This paper gives the investigation on surface integrity of rough machining of titanium alloy Ti–6% Al–4% V with uncoated carbide cutting tools. The experiments were carried out under dry cutting conditions. The cutting speeds selected in the experiment were 100, 75, 60 and 45 m min −1 . The depth of cut was kept constant at 2.0 mm. The feed rates used in the experiment were 0.35 and 0.25 mm rev −1 . Two types of insert were used in the experiments. For a range of cutting speeds, feeds, and depths of cut, measurements of surface roughness of machined surface, microhardness and work hardening backed up with scanning electron microscope were taken. The surface of titanium alloy is easily damaged during machining operations due to their poor machinability. The machined surface experienced microstructure alteration and increment in microhardness on the top white layer (≤10 μm) of the machined surface. Severe microstructure alteration was observed when machining with the dull tool. In addition, surface roughness values obtained were within the limit (